Vehicles using an engine, which uses gasoline, diesel oil, and the like as an energy source, as a driving source are a general vehicle type. However, the vehicles increasingly require new energy sources due to various factors such as the environmental pollutions of the energy sources for vehicles and the reduction in oil deposits. At present, one of technologies which are the closest approach to commercialization drives vehicles using electricity as an energy source.
However, unlike the existing vehicles having an engine using petroleum as an energy source, electric vehicles may not use a heating system using cooling water. That is, the existing vehicles having the engine using petroleum as an energy source as a driving source have considerable heat generated from the engine, include a cooling water circulation system for cooling the engine, and allow the cooling water to use heat absorbed from the engine for indoor heating. However, since driving sources used in the electric vehicles do not generate heat as much as that generated from the engine, the electric vehicles have a limit of using the existing heating scheme.
Therefore, various researches for electric vehicles having a heat pump added to an air conditioning system and, using the heat pump as a heat source, or including a separate heat source such as an electric heater, or the like have been conducted.
As illustrated in FIG. 1, a heat pump system for vehicles is configured to include a compressor 30 compressing and discharging a refrigerant, a high pressure heat exchanger 32 radiating the refrigerant discharged from the compressor 30, a first expansion valve 34 and a first bypass valve 36 provided in a parallel structure to selectively pass the refrigerant passing through the high pressure heat exchanger 32, an outdoor machine 48 heat-exchanging the refrigerant passing through the first expansion valve 34 or the first bypass valve 36 outdoors, a low pressure heat exchanger 60 evaporating the refrigerant passing through the outdoor machine 48, an accumulator 62 separating the refrigerant passing through the low pressure heat exchanger 60 into a gaseous refrigerant and a liquefied refrigerant, an internal heat exchanger 50 exchanging heat between the refrigerant supplied to the low pressure heat exchanger 60 and the refrigerant returning to the compressor 30, a second expansion valve 56 selectively expanding the refrigerant supplied to the low pressure heat exchanger 60, and a second bypass valve 58 provided in parallel with the second expansion valve 56 to selectively connect an outlet side of the outdoor machine 48 to an inlet side of the accumulator 62.
In FIG. 1, reference numeral 10 represents an air conditioning case in which the high pressure heat exchanger 32 and the low pressure heat exchanger 60 are embedded, reference numeral 12 represents a temperature control door controlling a mixed amount of cold air with hot air, and reference numeral 20 represents a blower provided at the inlet of the air conditioning case.
According to the existing heat pump system for vehicles configured as described above, when a heat pump mode (heating mode) is operated, the first bypass valve 36 and the second expansion valve 56 are closed and the first expansion valve 34 and the second bypass valve 58 are opened. Further, the temperature control door 12 is operated as illustrated in FIG. 1.
Therefore, the refrigerant discharged from the compressor 30 sequentially passes through the high pressure heat exchanger 32, the first expansion valve 34, the outdoor heat exchanger 48, a high pressure part 52 of the internal heat exchanger 50, the second bypass valve 58, the accumulator 62, and a low pressure part 54 of the internal heat exchanger 50 and then returns to the compressor 30.
That is, the high pressure heat exchanger 32 serves as a heater and the outdoor machine 48 serves as an evaporator.
When an air conditioner mode (cooling mode) is operated, the first bypass valve 36 and the second expansion valve 56 are opened and the first expansion valve 34 and the second bypass valve 58 are closed. Further, the temperature control door 12 closes a passage of the high pressure heat exchanger 32.
Therefore, the refrigerant discharged from the compressor 30 sequentially passes through the high pressure heat exchanger 32, the first bypass valve 36, the outdoor heat exchanger 48, the high pressure part 52 of the internal heat exchanger 50, the second expansion valve 56, the low pressure heat exchanger 60, the accumulator 62, and the low pressure part 54 of the internal heat exchanger 50 and then returns to the compressor 30. That is, the low pressure heat exchanger 60 serves as the evaporator and the high pressure heat exchanger 32 closed by the temperature control door 12 serves as the heater like the heat pump mode.
As the related technology, Korean Patent Laid-Open Publication No. 10-2012-0103054 (Published on Sep. 19, 2012, Title: Heat Pump System For Vehicles) is disclosed.
Meanwhile, in the heating mode, surface temperature is rapidly reduced while the outdoor heat exchanger absorbs ambient heat in a state in which external temperature is low, and as a result moisture on the surface is frozen to generate frost and condensed water is discharged during a defrosting process of melting the frost.
The outdoor heat exchanger which is a cross flow type has a problem in that when fins/tubes are disposed, draining property of water melted during the defrosting process of melting frost is bad and thus the defrosting is not made well and the melted frost is re-frozen and thus the frosting occurs.
On the other hand, like the general evaporator for vehicles, the down flow type outdoor heat exchanger is formed to make the melted frost flow down, thereby making the draining property good and improving the efficiency of the defrosting mode of the heat pump.
However, even in the down flow type outdoor heat exchanger, the frosting is generated, but as illustrated in FIG. 2, a refrigerant flux is small in some paths in which the channel is changed upon the heating mode and thus an area in which the frosting is not generated may be confirmed. The reason is that since the gaseous refrigerant is changed to the liquefied refrigerant upon the cooling mode but the liquefied refrigerant is changed to the gaseous refrigerant upon the heating mode, when the same path is used, a flux distribution of a refrigerant is non-uniform inside a core and thus a non-generation area F of frosting occurs.
A down flow type outdoor heat exchanger 1′ illustrated in FIGS. 2-3 has four paths. Here, tubes 300′ are distributed for each path so that the number of columns of the tubes 300′ is gradually reduced from a first path toward a rear end.
Describing an outdoor heat exchanger having tubes of 81 columns in total, the tubes are distributed at a ratio of 30:24:15:12=1 path:2 path:3 path:4 path. In this case, as a frosting test result, it may be confirmed that the non-generation area of the frosting occurs approximately in an area of a latter part 18% of the 1 path and an area of a starting part 57% of the 2 path.
The frosting in the heat pump system is preferable to be maximally delayed and is more preferable to uniformly appear on the whole surface of the heat exchanger without being concentrated toward a specific portion of the surface in terms of performance.
Therefore, an outdoor heat exchanger for a heat pump capable of maximally delaying frosting needs to be developed.